Control device



March 22, 1938. N. c. SCHELLENGER 2,111,309

CONTROL DEVICE Filed Oct. '7, 1933 3 Sheets-Sheet l I nun-"nu March1938. N. c. SCHELLENGER 2,111,309

CONTROL DEVICE Filed 001;. 7, 1933 3 Sheets-Sheet 2 Inventor.- [YewtorzCScizeZZem e72 March 22, 1938. 1 scHELLENGER 2,111,809

CONTROL DEVICE Filed 001;. 7, 1933 3 Sheets-Sheet 3 [72 2/972 tor.Newton fficizeZZ eager which will be inexpensive to and practicable ofmanufacture.

Another object of the invention is the provision, in a variableresistance device of the type having an arcuate resistance element and acontactor actuated by an arm for movement over the surface of theresistance element, of a novel type contactor and a novel supporting andactuating mechanism therefor.

Another object of the invention is the provision, in a variableresistance device, of a novel resistance element which has greatdurability and which will not change materially in electricalcharacteristics throughout a long period of use even though subjected toadverse conditions such as heating, moisture, vibration and the like.

Other objects of the invention will appear from the followingdescription takenin connection with the accompanying drawings, wherein:

Fig. 1 is a side elevational view partly in crosssection showing, by wayof illustration, a combined switch and variable resistance deviceembodying the invention;

Fig. 2 is an end elevational view of the'variable resistance device withthe casing member removed;

Fig. 3 is a top plan view ofthe variable resistance device, with oneportion of the casing removed and portions .of the parts broken away toshow the construction;

Fig. 4 is an exploded view of the rheostat portion of the device, theswitch and its housing being omitted;

Fig. 5 is an enlarged fragmentary side elevational view, partly incross-section, showing certain details of construction;

Figs. 6, '7, and 8 are enlarged diagrammatic fragmentary views, withcertain proportions exaggerated, illustrating the operation of a portionof the device;

Fig. 9 is a top plan view showing the base member with one terminal inposition; and

Fig. 10 is a fragmentary enlarged view, partly in cross-section, showinga portion of the resistance element.

In Fig. l is shown a combined rheostat and switch device consisting of arheostat unit I including metallic cup-like casing member 2 and a switchunit 3 including a cup-like casing member 4 formed of insulatingmaterial and secured to the outside of the rheostat casing member 2.

The rheostat I with the casing member 2 removed is shown in Figs. 2 and3 and comprises a disc-like base member 5 formed of insulating materialand having thereon a flat annular coating of carbonaceous coatingmaterial, the top surface portion of the base member 5 thus constitutinga resistance element 5. Two terminal members I, 8 are locked by means ofintegral, laterally extending wing portions, in slots 9, i5 formed in alaterally projecting portion I l of the base member 5 and are secured tothe base 5 by rivets I2,

I9, which latter constitute electrical connections between the terminalmembers I, 5 and the end portions of the resistance coating 5,respectively.

A third terminal member I4 is disposed between the other terminalmembers 1, I, and is likewise locked in a slot l5 and is secured to thebase member 5 by a rivet I5, the rivet I5 passing through a perforationH in a laterally projecting portion ll of an annular current collectorl9, disposed on the same side of the base 5 .as the resistance coating5.

The base member, 5 is provided with an axial perforation 20 throughwhich extends a cylindrical bushing 2| having on one end a shoulder 22lying against the base 5, the edge of the shoulder 22 being knurled toprovide a series of teeth 23 which bite into the base member 5 to securethe bushing 2| against rotation in the base member .5; this bushing hasat'lts other end a threaded extension 24 to receive a mounting nut (notshown); the bushing 2| is secured to the base member 5 by a frictionwasher 25 which latter is locked on the bushing 2| by peening or swagingan edge of the bushing against the washer 25.

The shoulder22 of the bushing 2| projects from the base member 5 toprovide a raised seat for the current collector l9 which latter isaxially alined with the bushing 2| and insulated therefrom by aninsulating washer 25. The current collector I9 has an openingconsiderably larger than the diameter of a shaft 29 and is positionedabout the shaft and prevented from contacting the same by a pair of ears21, 28 which engage the periphery of washer 25. The washer 25 isprovided with 'an opening to fit snugly about the shaft.

The shaft 29 is journaled in the bushing 2| and has a flattened endportion-9|l carrying a flat plate-like actuator 3| formed of insulatingmaterial and seated against the shoulder formed by the flattened portion30 of the shaft 29. A washer 92 against which the end 9|! of the shaft29 is riveted, clamps the actuator 3| against the shoulder. The actuator9| lies in a plane parallel to the plane of the base member 5 and spacedtherefrom. Extending from the actuator 3| and parallel to the axis ofthe shaft 29 is a metallic pin 39 positioned to engage a switchactuating cam 94 constituting a portion of the switch unit 9..

Disposed in contact with the resistance element 5, and arranged to sweepover the surface thereof, is a contactor formed of a thin strip of metaland having a curved portion 35, the bottom surface of this portion beingthereby adapted to make line contact with the surface of the resistanceelement 5, which line extends radially of the resistance element 5, andtransversely of the direction of movement of the contactor 35 on theresistance element 5. A pair of oppositely disposed ears 31, 35 extendsfrom the side'edges of the curved portion 95 of the contactor 35. Theend portions of the ears are straight and are bent inwardly and formedwith right angle bends whereby the extreme end portions lie in a planesubstantially parallel to the plane of the actuator member 3| and theportions adjacent the extreme end portions lie substantially in parallelplanes at right angles to said extreme end portions. The end portions ofthe ears 91, 35 are bent around a neck 99 of the actuator formed byoppositely disposed slots 45, 4|, and are positioned to be engagedalternately thereby to pull or draw the contactor from a point spaced inadvance of the line of contact between contactor and resistance eleintoflrm contact with the resistance element 5. The conductor 42 ispositioned by a pair of ears 44, 45 bent up from diametrically spacedpoints on the annular portion and entering; suitably positioned notches46, 41 formed in the actuator.

A warped spring washer 48 having notched, radially projecting ears 49,is interposed between the actuator 3| and the conductor 42 for pressingthe latter against the current collector l9 and is positioned by theears 44, 45 of the conductor 42 which extend through the notched ears49, 50 in the washer 48. The shaft 29 is held in the bushing 2! by asplit washer 5i en gaging a peripheral slot 52 formed in the shaft 2%and is spaced from the end of the bushing 2i by a thrust washer 53.

The arm 43 of the conductor 42 and the annular portion adjacent the arm43 are offset from the plane of 'the remainder of the annular portionwhich raises the juncture of the arm 43 and annular portion out ofcontact with the collector it thereby giving the arm a greater freelength; thus increasing its range of spring movement and making thepressure it will exert upon the contactor 35 less critical ofadjustment.

The rheostat member is assembled in the casing member 2, the side wallof which supports an insulating strip 54, the base member 5 constituting with the casing member 2 a rheostat housing. The switch unit 3 issuitably mounted in the end wall of the casing member 2, the switchactuating cam 34 extending through a perforation 55 in the end wall ofthe casing and lying in the path of movement of the pin 33.

The manner of employing and the operation of the device is as follows:

The rheostat unit i may be connected as a voltage divider, in which casethe side terminals 'u, 8 and the center terminal 84 are connected to thecircuit conductors (not shown). if the rheostat unit l is to be employedas a simple rheostat, only one of the side terminals (1, for example)and the centerterminal it; are connected to the proper circuitconductors (not shown). p

The effective resistance connected in the crcuit is adjustably varied byrotating the shaft which, through the agency of the actuator Eli andconductor 42, pulls or draws the contactor along the surface of theresistance coating 6 to a position wherein there will be connectedbetween the contactor 35 and the terminal l a length of the resistanceelement 5 corresponding to the desired resistance whereby the desiredamount of resistance is connected between the terminal and the contactor3%.). I

The electric circuit may be traced from the side terminal i through theresistance element 6 to the contactor 35, from'the contactor 35 throughthe conductor 42 to the current collector i9 and through the latter andits securing rivet it to the center terminal it. It the rheostat l isconnected as a voltage divider, there is, in addition, a circuit from.one side terminal ('i, for example) to the other through the resistanceelement.

In Fig. 6 is shown certain of the parts in the positions which theyassume, during the rotation ofthe shaft 29 in a counter-clockwisedirection, (as viewed in Fig. 3). It will be seen that the actuator 3ibears againstthe leading ear 38 of the contactor 35 to exert a draggingaction upon the contactor 35, drawing the latter over the surface of theresistance element 5. The contactor 35, which is driven by the neckportion 353 of the actuator 3| engaging the upstanding ears ill, 355 oithe contactor, assumes the position shown in Fig. 6. In this position,the plane (A-A) which includes the center-line of curved portion 33 ofthe contactor 35 intersects the top surface of this portionof thecontactor 35 at a point (a) lying between the point of contact (b) ofthe conductor 42 with the top surface of the contactor 35, and the pointof intersection (0) between the top surface of the contactor 35 and theplane (0-0) which plane passes through the point (0') where the bottomsurface of the contactor 35 touches the resistance element When theshaft29 is rotated in the opposite direction (clockwise, as viewed in Fig.3), the parts are moved t6 the positions shown in Fig. 8. During thismovement, as the actuator 3i is moved away from the now trailing ear 38of the contactor 35, the conductor 42 does not move with the actuator3!, because of the play provided between the ears 3?, 38 of thecontactor 35 and the actuator 30, and the conductor 4? presses againstthe top surface of the contactor 35 at a point (2)) on the portion ofthe contactor 35 that is out of contact with the resistance element 8and causes the contactor 35 to rock on the resistance element 5 towardthe position shown in Fig. 8. The friction between the spring washer 48and the actuator 3i is less than the friction between the conductor 42and the current collector l9, whereby the conductor i2 is not moveduntil the ears 4 45 thereof are engaged by the edges of the slottedportions of the actuator 3 i Prior to the time the ears M, 45 of theconductor are engaged by the edges of the slotted portions of theactuator til, the neck portion 39 of the actuator 3i engages the nowleading ear 3? of the contactor 3E) and draws the contactor 35 along theresistance element 6, the conductor d2 remaining stationary with respectto the resistance element 6, thus effecting a wiping action between thesurface of the conductor t2 and the upper surface of the contactor tothereby clean and polish the contact areas. Upon continued movement in asingle direction by the actuator 35, the

. ears i t?) of the conductor engage the edges of the slotted portionor" the actuator 38 and the contactor and conductor 32 are moved as aunit, the latter serving to maintain a steady pressure of the contactor35 against the resistance element and also serving to conduct thecurrent from the contacto'l' 3'5 to the current collector When the earsd5 of the conductor are engaged by the notched portions of the actuator33 i, the parts assume the positions shown in Fig. 8, wherein theactuator 36 bears against the now leading ear ill and the conductor Q2bears upon the top surface of the contactor 35 at a point back of thecenter-line of the contactor 352-. It will be seen that the parts havethe same relative positions as shown in 7 except that the positions arereversed.

From the foregoing it will be seen that this in vention provides avariable resistance device or rheostat wherein the contactor makes linecontact with the resistance element in a direction transverse to theline of movement of the contactor.

Such an arrangement insures that the length of resistance elementconnected between the contactor and the respective terminals will varyin a predetermined manner as the contactor' is moved over the surface ofthe resistance element. it will be seen that there can be no undesiredvariations in the effective length of the resistance element in high andlow spots in the contacting surfaces. Since the line of contact extendsin a direction normal to the direction of movement of the contactor, theonly shift in the effective point of contact is along this line andhence no appreciable change in the length of effective resistance cantake place except that due to the predetermined movement of thecontactor.

' The conductor exerts a force to press the contactor into engagementwith the resistance element and hence a large number of points on thecontact and lying along the line of contact with the resistance elementare brought into engagement with the resistance element. Since thecontactor is not rigidly fixed to the actuator and since the conductorbears upon only a small area of the top surface of the contactor, thelatter is free to rock laterally to accommodate itself to anyirregularities in the surface of the resistance element.

Inasmuch as the conductor presses the contactor firmly against theresistance element and the arm of the conductor has a relatively longfree-swinging length, there is no appreciable tendency for the contactorto bounce, whether induced by the roughness of the surface of theresistance element or due to vibration of the rheostat, but a uniformpressure is maintained.

Certain changes may be made in certain features of the constructionwithout affecting the operation or novel advantages. For example, thelost motion between the conductor and the actuator may be eliminated andthe conductor fixed rigidly to the actuator. In this case, the conductorwill not ride up on the contactor as explained in the foregoing but willserve to press the contactor against the resistance element and willelectrically connect the contactor with the circuit; furthermore, therewill also be a wiping action between the conductor and the contactorsince the conductor will be drawn across the surface of the contactor asthe actuator moves out to engage either of the angle portions of theears of the contactor.

In Figs. 9 and 10 is shown the base member and one of the cooperatingterminals. The base comprises a flat disk of insulating material 5having perforations 58, 51, 58 extending therethrough to accommodate theterminal rivets I2, I 3, ,i 6. The perforations 58, 51 are countersunkto receive the beveled head portions'of the rivets l2, I3 whereby thetops of the head portions lie flush with the top surface of the basemember 5.

.Before the terminals 1, 8 and H are assembled in the base member 5, thelatter is shielded at the central and marginal portions thereof and acarbonaceous conducting material is sprayed on the top surface of thebase member 5 and on the surfaces of the countersunk portions of theperforations 56, 51 to deposit a conductive layer having an annularshape, as shown.

The coating material comprises finely divided conductive particles, forexample,of graphite, dispersed in a suitable binder. The binder is ahard, smooth and non-hygroscopic material which will not deteriorate,wear unduly, or suffer a change in its electrical characteristics underadverse conditions of electrical use, friction, temperature, relativehumidity or vibration and which has no tendency to check, peel or raisefrom the supporting member. Compositions of the vinyl resin group, forexample, the composition commercially known as Vinylite, andcompositions of the nitrated cellulose group, such as pyroxylin aresuitable for use as a binder.

Alternatively, the central portion only of the base member 5 isshielded, and the layer on the marginal portion of the base member 5 isscraped off in a suitable manner, as with a scratch brush.

The terminal 8 is attached by the rivet it which is seated in theperforation 51 with its beveled edge pressing against the coated,countersunk portion of the perforation 51 whereby good electricalcontact is made between the head of the rivet l3 and the conductingmaterial. The top surface of the head of the rivet I3 is only slightlybelow the surface of the resistance element 8 and thus a substantiallyuniform contact pressure is insured between the contactor 35 and theresistance element 6 as the contactor 35 is moved over the surface ofthe resistance element and onto the top surface of the rivet I3.

Alternatively, instead of the foregoing type of resistance element,there may be provided a resistance element of the type disclosed incertain of my copending applications and comprising a strip of papercoated with the carbonaceous conducting material and adhesively securedto the base member.

It will be understood that, in the foregoing and in the appended claims,the expression line contact is not to be limited to a theoretical line,that is, a mathematical entity having length but no breadth. It isobviousthat such a result can not practically be achieved and thereforethe expression line contact" is to be taken to mean a line of contacthaving no appreciable breadth and as near to a theoretical line as ispracticable to produce.

While I have shown and described the invention with particular referenceto a combined switch and variable resistance unit for use in radio sets,the invention is not limited thereto and it is obvious that theinvention advantageously may be practiced in any variable resistancedevice of the same general type, whether large or small, single ormultiple unit, or whether alone or combined as a unit with otherelectrical devices or whether for use in radio or in other electricalcircuits' I claim:

1. In a variable resistance device, a resistance element, acontactorbearing upon said resist ance element, actuating means including a drivemember for effecting sliding movement between said contactor and saidresistance element, a conducting element disposed in contact with saidcontactor and lost motion means connecting said contactor and saidconducting means to said drive member whereby upon movement of saidactuating element relative to said resistance element, said contactor issubjected to a rocking movement upon said resistance element, saidconducting element being movable relatively to said contactor and alongthe surface thereof and said contactor and said conducting element beingmovable relatively to said resistance element.

2. In a variable resistance device, in combination, a resistanceelement, a contactor having a curved surface positioned to bear uponsaid resistance element, an actuating element for drawing said contactorin sliding contact with respect to said resistance element,.a conductingelement disposed to bear upon said contactor, means mounting saidconducting element for limited sliding contact with respect to saidcontactor, and means actuated by the movement of said actuating elementrelative to said resistance element for effecting a rocking movement ofsaid contactor on said resistance.

3. In a variable resistance device, a lease, fiat resistance meansthereon, a contact shoe having a curved surface bearing upon saidresistance means, and having substantially line contact therewith, ashaft extending through said base, an actuator on said shaft andpositioned to en gage said contact shoe for effecting sliding contactrelative to said resistance means in a di rection'transverse to the lineof contact between said shoe and said resistance means, a currentcollecting element carried by said base, a spring conductor bearingagainst said contact shoe against said current collecting element, meansconnecting said contact shoe to said actuator and effective uponmovement of said actuator, to rock said shoe relative to said resistancemeans, and means connecting said conductor to actuator and effective,upon a predetet iuned tent of movement of said actuator, r moving saidspring conductor relative to s l contact shoe.

In a variable resistance device, hase, re istance means fixed thereto, aextending through said base, an actuator on said shaft and movablerelative to said resistance a contact shoe formed to make substan allyline contact with said resistance means transversely of the line ofmovement of said shoe relative to said resistance means, lost motionmeans connecting said shoe to said actuator for efiecting movement ofsaid contact slice on said resistance meansconsequent to the initialmove ment of said actuating arm from rest in any position, a springconductor, and a second lost rug--- collector ing the l of electricalconneca between s contactor.

*l. a stance device, in

nation, a resistance tinned for slit are so 2168 elem la, a r'condueting actuator: pulling said contac merit, and tor spaced lent, acontactorco. ssing' contactor against sat contactor 130i engagein '1said resistan actuating including an member for p ing sa d contactorover s sistance element, a resilient current conductor engaging theco-ntactor and press ng contactor against said resistance ele tion, aresistance el v.ent, a contactor positioned on said resistance element,act: ing means including an insulating member for imparting motion tosaid contactor, a resilient an nular conductor having an arm extendingtherefrom for pressing said contactor against said r sistance element,said and a portion oi said annular conductor being offset from the remainder of said annular conductor for increas ing the range andefiectiveness of said spring arm.

NEWTON C.

